Okay, you've tried a bunch of times, without success. I'm going to *suggest* a couple things, with the knowledge that these suggestions are what I used to TRANSITION to just nicotine. You are using a sub-ohm coil, so I'm not sure I'd recommend going UP on the nicotine, necessarily.
If you haven't tried WTA (Whole tobacco Alkaloids) that might be a thing to try. I did this because, no matter what I did, by about 3 p.m. I'd get a sensation like having ants crawling all over me and just wanting to *stab* something. You can find threads about it fairly easily on here about that with the search function. Sounds like you have a few tanks, so when you are DYING for a cigarette, I'd suggest loading one tank with regular juice, then adding a *small* amount of WTA juice to the other. Like half a dropperful. There are a few vendors, Aroma is the one I used, it's expensive like crazy, but not crazy like buying YET another MOD. Keep the tank with you and put a squirt of WTA (I used the straight unflavored, 24 mg, but you're using a tiny amount, and the idea is to use it when you get to THAT point), which occurred later and later in the day for me. I am slowly weaning myself, and probably won't buy more. That said, if I'm heading into say, oral surgery, LOL, that might be a time I would use some WTA juice.
Your other option (likely cheaper) is to try Nic Salts which more closely mimic the nicotine found in cigarettes. Less expensive and when I tried it I preferred it, so that's what I bought as my Big Nic Stash. A little more expensive, but since I don't vape MORE of it than other forms of nicotine, *I* feel fine with it. I still enjoy regular juice, it's just that this is my preference. Again, maybe try ordering a small bottle and my thought is you might be able to go higher on the nic because it is smoother, not harsh, but you'll still get a throat hit. That might help with the transition. If you genuinely prefer it, you can certainly choose if this is your main deal, and decide to DIY with that form of nic. I think it's a personal choice.
Those are some things I can think of to *try* given that you're getting very frustrated. I was very motivated to vape and willing to do whatever it took to get there, this try around. I approached it as "Nothing could possibly be more harmful than 2--3 ppd and being told I was headed into COPD land."
Doing it in a stage fashion for me was very helpful, because my brain HATES changes. Also, I was buying expensive stuff and it motivated me further not to smoke.
Again, this is a personal choice, it's not a recommendation, but it is what worked for ME. Ppl who struggle with harshness/getting enough nic seem to do well with Nic Salts, and that was the case for me. I just really do well with them, but it should again be noted that I am taking a calculated risk by inducing those things, and continuing to use nic salts, but you have to do what works for YOU and decide if it's more or less risky than smoking.
I wish you all the best, and I feel your pain. I have a bunch of vape equipment lying around from former quit attempts going back 10 years. I'm a hard case, but the first day without smoking was liberating.
Also, look for ways to reward yourself. I didn't even know *how* to reward myself at first, I was so used to smoking as a reward. I had to sit myself down and make a list. It might be getting your car detailed after your first couple weeks, it might be buying something you coveted, it might be coming on here and boasting about your progress (LOL, I just did that earlier today

) starting an enjoyable activity, exercising, whatever.
Also, forget about your past attempts. I had to. I had to remind myself that *every quit is different* and that failing in the past didn't mean failing in the future. You can do this.
Anna